1. Field of the Invention
This invention relates to a novel fuel oil composition, and more specifically to a fuel oil composition for diesel engines, which comprises a mineral oil as a principal component and (a) 2-13 wt % of one or more dialkyl phthalate compounds and (b) 2-13 wt % of one or more glycol ether compounds, the total content of both types of the compounds is from 4 to 15 wt %.
2. Prior Art
Mounted in automobiles, ships and construction machineries, diesel engines are widely spread in the world and still tend to increase year after year in number. Keeping in step with this, there is an increasing demand for diesel engine fuel oil. It is therefore essential to take measures such as conversion of straight run gas oil into heavier one(s) and blended use of cracked gas oil in straight run gas oil. These measures, however, lower the cetane number of gas oil, leading to deterioration in the ignitability in diesel engines. These measures also lead to discharge of still more hydrocarbons, carbon monoxide, nitrogen oxides, sulfurous gas and particulate matters in exhaust gas from diesel engines. From the viewpoints of assurance of normal operation of diesel engines and prevention of air pollution, there are strong social desires for the retention of a high cetane number and reduction of these emission matters.
Concerning gas oil, its cetane number has conventionally been maintained at a necessary level by limiting the extent of conversion of straight run gas oil into heavier one(s), controlling the blending ratio of cracked gas oil to straight run gas oil, or adding an ignitability improver to gas oil. For example, Japanese Patent Application Laid-Open (Kokai) No. SHO 59-207988 discloses a fuel composition added with 0.1 wt % or more of an alkyl nitrate or dialkyl phthalate to improve the ignitability of light gas oil. It also discloses that the addition of the alkyl nitrate permits earlier ignition and at the same time, lowers the rate of a pressure rise upon combustion, thereby including smooth combustion, reducing engine noise and vibrations and improving the quality of diesel smoke.
With a view to reducing emission matters from diesel engines, a great deal of effort has also been made in many aspects, including improvements in the configurations of combustion chambers, exhaust gas recirculation systems, exhaust-gas-cleaning catalytic converters, particulate trap systems, and the quality of fuel oil and lubricating oil. Nonetheless, no sufficient reducing effects have been achieved yet in economy and also in the stability of performance over a long term.
An improvement in the quality of fuel oil has attracted interests as an effective method for the reduction of emission matters because it practically requires no change to the mechanism of diesel engines. For example, Japanese Patent Application Laid-Open (Kokai) No. HEI 3-234793 discloses that fuel oil, which contains dimethylacetal in mineral oil, discharges extremely little black smoke and NO.sub.x and has good ignitability and thermal efficiency. From the economical viewpoint, however, it is difficult to always use a diesel engine fuel oil which contains dimethylacetal in a large quantity.
Japanese Patent Application Laid-Open (Kokai) No. HEI 4-213391 discloses a fuel oil for diesel engines, which makes use of a diesel fuel additive composed of perbasified calcium sulfonate dispersed in an organic solvent. Japanese Patent Application Laid-Open (Kokai) No. HEI 7-70570 discloses one making use of a fuel additive which contains a peroxide of a metal salt of an organic acid. When fuel oil burns, a metal-containing additive itself is discharged as ash in exhaust gas, resulting in the problem that it causes harm to the human body.
Further, Japanese Patent Application Laid-Open (Kokai) No. SHO 59-207988 discloses a fuel composition which contains 0.1 wt % or more of an alkyl nitrate or dialkyl phthalate added to improve the ignitability of light gas oil. It is also disclosed in this Kokai publication that a fuel composition added with a dialkyl phthlate promotes initial combustion to achieve complete combustion and prevents occurrence of smearing. It is, however, difficult to reduce the discharge of particulate matters, which occur under diverse operation conditions of a diesel engine in actual use, by only promoting the initial combustion of the fuel composition.
As has been described above, none of the conventional techniques was able to provide a fuel oil composition for diesel engines, which comprises a mineral oil as a principal component, has a high cetane number and substantially reduces the discharges of particulate matters (hereinafter also called "PM") and carbon monoxide (hereinafter called "CO") in exhaust gas.
It would be an improvement over the above-described conventional art to provide a fuel oil for diesel engines, which has good ignitability owing to the possession of a high cetane number and reduces the discharges of PM and CO in exhaust gas upon combustion.